Display screen or portion thereof with a graphical user interface



FIG. 1 is a front view of a first embodiment of a display screen or portion thereof with a graphical user interface; and,

FIG. 2 is a front view of a second embodiment of a display screen or portion thereof with a graphical user interface.

The outermost broken lines in the figures show a display screen or portion thereof, and form no part of the claimed design. The diagonal broken lines are shading which form no part of the claimed design. 

CLAIM We claim the ornamental design for a display screen or portion thereof with a graphical user interface, as shown and described. 